A rectangular tem waveguide with photonic crystal walls for excitation of quasi-optical amplifiers

Thin photonic crystal substrates are used to produce a TEM mode in a rectangular waveguide. Hexagonal pads arranged in honeycomb lattice and connected to the ground plane by substrate vias form the photonic crystal waveguide walls. Measurements on a Ku-band waveguide with two photonic crystal sidewalls showed a Field Flatness Efficiency (FFE) of better than 80% between 14.9 and 15.4 GHz, a substantial increase compared to the 50% of conventional rectangular waveguide. Simulations of a striped photonic crystal show similar behavior with additional property that it is also possible to use the crystal on top and bottom walls. Such a waveguide could support dual cross-polarized TEM modes by preventing only the longitudinal magnetic fields at the crystal surface.